The present invention relates to a method of removing a particle of a photomask by applying an atomic force microscope technology.
A micromachining technology of a nanometer order is requested for high function formation and high integration formation, and research and development of a machining technology of local anodic oxidation or microscratch machining using a scanning probe microscope (SPM) are intensely carried out. Not only a pursuit for a possibility of micromachining but also a pursuit for machining of an accurate shape or with high accuracy have been requested.
For example, recently, in an apparatus on the basis of an atomic force microscope (AFM), high accuracy correction of a micropattern surplus defect of a photomask is carried out by microscratch machining in which scanning is carried out with exerting a high press force (high load) on a stylus harder than a material to be machined and physical removal is carried accordingly for machining (Nonpatent Reference 1).
In accordance with a progress in miniaturization of lithography, a size of a particle to be removed on a silicon wafer becomes small, a and sufficient resolution cannot be obtained an optical microscope so that the particle is now observed by a scanning electron microscope or an atomic force microscope. Although removal of a particle is heretofore dependent on removal by cleaning, in the case of a small number of particles, the silicon wafer may conversely be contaminated at a cleaning step, and a method of effectively removing a small number of particles has been requested. Recently, there is also reported a method of applying an atomic force microscope technology used for observation as a method of removing a small number of fine particles on a silicon wafer (Nonpatent Reference 2).
Similar to the silicon wafer, also in the case of a photomask, with increased miniaturization of lithography, a size of a particle to be removed becomes small and a method of removing a particle which cannot be removed by cleaning is requested. When a particle is present at a photomask before being pasted with a pellicle, even when the number of particles is small, defects are produced in all of patterns to be transcribed and therefore, the particles need to be removed completely. There are various kinds of particles on a photomask such as a metal, a glass bump, a resist residue and the like and in order to ensure an optical property, there has been requested a method of removing a particle without damaging a quartz or glass substrate of a matrix as much as possible.
In order to remove a particle, it is necessary to know the kind of the particle since a method of removing a particle differs by the kind of the particle. There has been known a method of pressing a diamond stylus having a sharp tip to a particle and predicting Young's modulus of the particle from bending of a cantilever or a depth of an impression produced by the pressing and predicting a material of the particle from a value of Young's modulus as an indentation method. Recently, there has been carried out a nanoindentation method for executing an indentation method by attaching a diamond stylus having a tip diameter equal to or smaller than 100 nm to an atomic force microscope as a new application of the atomic force microscope as a method of predicting a material by calculating a hardness of a small region. The method provides a function of predicting a material of even a small object of a particle or the like.
[Nonpatent Reference 1] T. Amanao, M. Nishiguch, H. Hashimoto, Y. Morikawa, N. Hayashi, R. White, R. Bozak, and L. Terrill, Proc. of SPIE 5256 538–545 (2003)
[Nonpatent Reference 2] Junichi Muramoto, Hitoshi Kuniyasu, Tsuyoshi Hattori, Proceeding of 51st Conference of Applied Physics No. 2, 31p-B-2, p856 (2004)
It is an object of the invention to reduce damage on a quartz or glass substrate in removing a small particle on a photomask using an atomic force microscope technology.